src/librustc_typeck/check/wfcheck.rs

   1 use crate::check::{Inherited, FnCtxt};
   2 use crate::constrained_generic_params::{identify_constrained_generic_params, Parameter};
   3
   4 use crate::hir::def_id::DefId;
   5 use rustc::traits::{self, ObligationCauseCode};
   6 use rustc::ty::{self, Lift, Ty, TyCtxt, GenericParamDefKind, TypeFoldable, ToPredicate};
   7 use rustc::ty::subst::{Subst, InternalSubsts};
   8 use rustc::util::nodemap::{FxHashSet, FxHashMap};
   9 use rustc::mir::interpret::ConstValue;
  10 use rustc::middle::lang_items;
  11 use rustc::infer::opaque_types::may_define_existential_type;
  12
  13 use syntax::ast;
  14 use syntax::feature_gate::{self, GateIssue};
  15 use syntax_pos::Span;
  16 use syntax::symbol::sym;
  17 use errors::{DiagnosticBuilder, DiagnosticId};
  18
  19 use rustc::hir::itemlikevisit::ParItemLikeVisitor;
  20 use rustc::hir;
  21
  22 /// Helper type of a temporary returned by `.for_item(...)`.
  23 /// This is necessary because we can't write the following bound:
  24 ///
  25 /// ```rust
  26 /// F: for<'b, 'tcx> where 'gcx: 'tcx FnOnce(FnCtxt<'b, 'gcx, 'tcx>)
  27 /// ```
  28 struct CheckWfFcxBuilder<'gcx, 'tcx> {
  29     inherited: super::InheritedBuilder<'gcx, 'tcx>,
  30     id: hir::HirId,
  31     span: Span,
  32     param_env: ty::ParamEnv<'tcx>,
  33 }
  34
  35 impl<'gcx, 'tcx> CheckWfFcxBuilder<'gcx, 'tcx> {
  36     fn with_fcx<F>(&'tcx mut self, f: F)
  37     where
  38         F: for<'b> FnOnce(&FnCtxt<'b, 'gcx, 'tcx>, TyCtxt<'gcx, 'gcx>) -> Vec<Ty<'tcx>>,
  39     {
  40         let id = self.id;
  41         let span = self.span;
  42         let param_env = self.param_env;
  43         self.inherited.enter(|inh| {
  44             let fcx = FnCtxt::new(&inh, param_env, id);
  45             if !inh.tcx.features().trivial_bounds {
  46                 // As predicates are cached rather than obligations, this
  47                 // needsto be called first so that they are checked with an
  48                 // empty `param_env`.
  49                 check_false_global_bounds(&fcx, span, id);
  50             }
  51             let wf_tys = f(&fcx, fcx.tcx.global_tcx());
  52             fcx.select_all_obligations_or_error();
  53             fcx.regionck_item(id, span, &wf_tys);
  54         });
  55     }
  56 }
  57
  58 /// Checks that the field types (in a struct def'n) or argument types (in an enum def'n) are
  59 /// well-formed, meaning that they do not require any constraints not declared in the struct
  60 /// definition itself. For example, this definition would be illegal:
  61 ///
  62 /// ```rust
  63 /// struct Ref<'a, T> { x: &'a T }
  64 /// ```
  65 ///
  66 /// because the type did not declare that `T:'a`.
  67 ///
  68 /// We do this check as a pre-pass before checking fn bodies because if these constraints are
  69 /// not included it frequently leads to confusing errors in fn bodies. So it's better to check
  70 /// the types first.
  71 pub fn check_item_well_formed<'tcx>(tcx: TyCtxt<'tcx, 'tcx>, def_id: DefId) {
  72     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
  73     let item = tcx.hir().expect_item_by_hir_id(hir_id);
  74
  75     debug!("check_item_well_formed(it.hir_id={:?}, it.name={})",
  76            item.hir_id,
  77            tcx.def_path_str(def_id));
  78
  79     match item.node {
  80         // Right now we check that every default trait implementation
  81         // has an implementation of itself. Basically, a case like:
  82         //
  83         //     impl Trait for T {}
  84         //
  85         // has a requirement of `T: Trait` which was required for default
  86         // method implementations. Although this could be improved now that
  87         // there's a better infrastructure in place for this, it's being left
  88         // for a follow-up work.
  89         //
  90         // Since there's such a requirement, we need to check *just* positive
  91         // implementations, otherwise things like:
  92         //
  93         //     impl !Send for T {}
  94         //
  95         // won't be allowed unless there's an *explicit* implementation of `Send`
  96         // for `T`
  97         hir::ItemKind::Impl(_, polarity, defaultness, _, ref trait_ref, ref self_ty, _) => {
  98             let is_auto = tcx.impl_trait_ref(tcx.hir().local_def_id_from_hir_id(item.hir_id))
  99                                 .map_or(false, |trait_ref| tcx.trait_is_auto(trait_ref.def_id));
 100             if let (hir::Defaultness::Default { .. }, true) = (defaultness, is_auto) {
 101                 tcx.sess.span_err(item.span, "impls of auto traits cannot be default");
 102             }
 103             if polarity == hir::ImplPolarity::Positive {
 104                 check_impl(tcx, item, self_ty, trait_ref);
 105             } else {
 106                 // FIXME(#27579): what amount of WF checking do we need for neg impls?
 107                 if trait_ref.is_some() && !is_auto {
 108                     span_err!(tcx.sess, item.span, E0192,
 109                               "negative impls are only allowed for \
 110                                auto traits (e.g., `Send` and `Sync`)")
 111                 }
 112             }
 113         }
 114         hir::ItemKind::Fn(..) => {
 115             check_item_fn(tcx, item);
 116         }
 117         hir::ItemKind::Static(ref ty, ..) => {
 118             check_item_type(tcx, item.hir_id, ty.span, false);
 119         }
 120         hir::ItemKind::Const(ref ty, ..) => {
 121             check_item_type(tcx, item.hir_id, ty.span, false);
 122         }
 123         hir::ItemKind::ForeignMod(ref module) => for it in module.items.iter() {
 124             if let hir::ForeignItemKind::Static(ref ty, ..) = it.node {
 125                 check_item_type(tcx, it.hir_id, ty.span, true);
 126             }
 127         },
 128         hir::ItemKind::Struct(ref struct_def, ref ast_generics) => {
 129             check_type_defn(tcx, item, false, |fcx| {
 130                 vec![fcx.non_enum_variant(struct_def)]
 131             });
 132
 133             check_variances_for_type_defn(tcx, item, ast_generics);
 134         }
 135         hir::ItemKind::Union(ref struct_def, ref ast_generics) => {
 136             check_type_defn(tcx, item, true, |fcx| {
 137                 vec![fcx.non_enum_variant(struct_def)]
 138             });
 139
 140             check_variances_for_type_defn(tcx, item, ast_generics);
 141         }
 142         hir::ItemKind::Enum(ref enum_def, ref ast_generics) => {
 143             check_type_defn(tcx, item, true, |fcx| {
 144                 fcx.enum_variants(enum_def)
 145             });
 146
 147             check_variances_for_type_defn(tcx, item, ast_generics);
 148         }
 149         hir::ItemKind::Trait(..) => {
 150             check_trait(tcx, item);
 151         }
 152         hir::ItemKind::TraitAlias(..) => {
 153             check_trait(tcx, item);
 154         }
 155         _ => {}
 156     }
 157 }
 158
 159 pub fn check_trait_item<'tcx>(tcx: TyCtxt<'tcx, 'tcx>, def_id: DefId) {
 160     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
 161     let trait_item = tcx.hir().expect_trait_item(hir_id);
 162
 163     let method_sig = match trait_item.node {
 164         hir::TraitItemKind::Method(ref sig, _) => Some(sig),
 165         _ => None
 166     };
 167     check_associated_item(tcx, trait_item.hir_id, trait_item.span, method_sig);
 168 }
 169
 170 pub fn check_impl_item<'tcx>(tcx: TyCtxt<'tcx, 'tcx>, def_id: DefId) {
 171     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
 172     let impl_item = tcx.hir().expect_impl_item(hir_id);
 173
 174     let method_sig = match impl_item.node {
 175         hir::ImplItemKind::Method(ref sig, _) => Some(sig),
 176         _ => None
 177     };
 178     check_associated_item(tcx, impl_item.hir_id, impl_item.span, method_sig);
 179 }
 180
 181 fn check_associated_item<'tcx>(
 182     tcx: TyCtxt<'tcx, 'tcx>,
 183     item_id: hir::HirId,
 184     span: Span,
 185     sig_if_method: Option<&hir::MethodSig>,
 186 ) {
 187     debug!("check_associated_item: {:?}", item_id);
 188
 189     let code = ObligationCauseCode::MiscObligation;
 190     for_id(tcx, item_id, span).with_fcx(|fcx, tcx| {
 191         let item = fcx.tcx.associated_item(fcx.tcx.hir().local_def_id_from_hir_id(item_id));
 192
 193         let (mut implied_bounds, self_ty) = match item.container {
 194             ty::TraitContainer(_) => (vec![], fcx.tcx.mk_self_type()),
 195             ty::ImplContainer(def_id) => (fcx.impl_implied_bounds(def_id, span),
 196                                           fcx.tcx.type_of(def_id))
 197         };
 198
 199         match item.kind {
 200             ty::AssocKind::Const => {
 201                 let ty = fcx.tcx.type_of(item.def_id);
 202                 let ty = fcx.normalize_associated_types_in(span, &ty);
 203                 fcx.register_wf_obligation(ty, span, code.clone());
 204             }
 205             ty::AssocKind::Method => {
 206                 reject_shadowing_parameters(fcx.tcx, item.def_id);
 207                 let sig = fcx.tcx.fn_sig(item.def_id);
 208                 let sig = fcx.normalize_associated_types_in(span, &sig);
 209                 check_fn_or_method(tcx, fcx, span, sig,
 210                                    item.def_id, &mut implied_bounds);
 211                 let sig_if_method = sig_if_method.expect("bad signature for method");
 212                 check_method_receiver(fcx, sig_if_method, &item, self_ty);
 213             }
 214             ty::AssocKind::Type => {
 215                 if item.defaultness.has_value() {
 216                     let ty = fcx.tcx.type_of(item.def_id);
 217                     let ty = fcx.normalize_associated_types_in(span, &ty);
 218                     fcx.register_wf_obligation(ty, span, code.clone());
 219                 }
 220             }
 221             ty::AssocKind::Existential => {
 222                 // do nothing, existential types check themselves
 223             }
 224         }
 225
 226         implied_bounds
 227     })
 228 }
 229
 230 fn for_item<'gcx: 'tcx, 'tcx>(
 231     tcx: TyCtxt<'gcx, 'gcx>,
 232     item: &hir::Item,
 233 ) -> CheckWfFcxBuilder<'gcx, 'tcx> {
 234     for_id(tcx, item.hir_id, item.span)
 235 }
 236
 237 fn for_id<'gcx: 'tcx, 'tcx>(
 238     tcx: TyCtxt<'gcx, 'gcx>,
 239     id: hir::HirId,
 240     span: Span,
 241 ) -> CheckWfFcxBuilder<'gcx, 'tcx> {
 242     let def_id = tcx.hir().local_def_id_from_hir_id(id);
 243     CheckWfFcxBuilder {
 244         inherited: Inherited::build(tcx, def_id),
 245         id,
 246         span,
 247         param_env: tcx.param_env(def_id),
 248     }
 249 }
 250
 251 /// In a type definition, we check that to ensure that the types of the fields are well-formed.
 252 fn check_type_defn<'tcx, F>(
 253     tcx: TyCtxt<'tcx, 'tcx>,
 254     item: &hir::Item,
 255     all_sized: bool,
 256     mut lookup_fields: F,
 257 ) where
 258     F: for<'fcx, 'gcx, 'tcx2> FnMut(&FnCtxt<'fcx, 'gcx, 'tcx2>) -> Vec<AdtVariant<'tcx2>>,
 259 {
 260     for_item(tcx, item).with_fcx(|fcx, fcx_tcx| {
 261         let variants = lookup_fields(fcx);
 262         let def_id = fcx.tcx.hir().local_def_id_from_hir_id(item.hir_id);
 263         let packed = fcx.tcx.adt_def(def_id).repr.packed();
 264
 265         for variant in &variants {
 266             // For DST, or when drop needs to copy things around, all
 267             // intermediate types must be sized.
 268             let needs_drop_copy = || {
 269                 packed && {
 270                     let ty = variant.fields.last().unwrap().ty;
 271                     fcx.tcx.erase_regions(&ty).lift_to_tcx(fcx_tcx)
 272                         .map(|ty| ty.needs_drop(fcx_tcx, fcx_tcx.param_env(def_id)))
 273                         .unwrap_or_else(|| {
 274                             fcx_tcx.sess.delay_span_bug(
 275                                 item.span, &format!("inference variables in {:?}", ty));
 276                             // Just treat unresolved type expression as if it needs drop.
 277                             true
 278                         })
 279                 }
 280             };
 281             let all_sized =
 282                 all_sized ||
 283                 variant.fields.is_empty() ||
 284                 needs_drop_copy();
 285             let unsized_len = if all_sized {
 286                 0
 287             } else {
 288                 1
 289             };
 290             for (idx, field) in variant.fields[..variant.fields.len() - unsized_len]
 291                 .iter()
 292                 .enumerate()
 293             {
 294                 let last = idx == variant.fields.len() - 1;
 295                 fcx.register_bound(
 296                     field.ty,
 297                     fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem),
 298                     traits::ObligationCause::new(
 299                         field.span,
 300                         fcx.body_id,
 301                         traits::FieldSized {
 302                             adt_kind: match item.node.adt_kind() {
 303                                 Some(i) => i,
 304                                 None => bug!(),
 305                             },
 306                             last
 307                         }
 308                     )
 309                 );
 310             }
 311
 312             // All field types must be well-formed.
 313             for field in &variant.fields {
 314                 fcx.register_wf_obligation(field.ty, field.span,
 315                     ObligationCauseCode::MiscObligation)
 316             }
 317         }
 318
 319         check_where_clauses(tcx, fcx, item.span, def_id, None);
 320
 321         // No implied bounds in a struct definition.
 322         vec![]
 323     });
 324 }
 325
 326 fn check_trait<'tcx>(tcx: TyCtxt<'tcx, 'tcx>, item: &hir::Item) {
 327     debug!("check_trait: {:?}", item.hir_id);
 328
 329     let trait_def_id = tcx.hir().local_def_id_from_hir_id(item.hir_id);
 330
 331     let trait_def = tcx.trait_def(trait_def_id);
 332     if trait_def.is_marker {
 333         for associated_def_id in &*tcx.associated_item_def_ids(trait_def_id) {
 334             struct_span_err!(
 335                 tcx.sess,
 336                 tcx.def_span(*associated_def_id),
 337                 E0714,
 338                 "marker traits cannot have associated items",
 339             ).emit();
 340         }
 341     }
 342
 343     for_item(tcx, item).with_fcx(|fcx, _| {
 344         check_where_clauses(tcx, fcx, item.span, trait_def_id, None);
 345         vec![]
 346     });
 347 }
 348
 349 fn check_item_fn<'tcx>(tcx: TyCtxt<'tcx, 'tcx>, item: &hir::Item) {
 350     for_item(tcx, item).with_fcx(|fcx, tcx| {
 351         let def_id = fcx.tcx.hir().local_def_id_from_hir_id(item.hir_id);
 352         let sig = fcx.tcx.fn_sig(def_id);
 353         let sig = fcx.normalize_associated_types_in(item.span, &sig);
 354         let mut implied_bounds = vec![];
 355         check_fn_or_method(tcx, fcx, item.span, sig,
 356                            def_id, &mut implied_bounds);
 357         implied_bounds
 358     })
 359 }
 360
 361 fn check_item_type<'tcx>(
 362     tcx: TyCtxt<'tcx, 'tcx>,
 363     item_id: hir::HirId,
 364     ty_span: Span,
 365     allow_foreign_ty: bool,
 366 ) {
 367     debug!("check_item_type: {:?}", item_id);
 368
 369     for_id(tcx, item_id, ty_span).with_fcx(|fcx, gcx| {
 370         let ty = gcx.type_of(gcx.hir().local_def_id_from_hir_id(item_id));
 371         let item_ty = fcx.normalize_associated_types_in(ty_span, &ty);
 372
 373         let mut forbid_unsized = true;
 374         if allow_foreign_ty {
 375             if let ty::Foreign(_) = fcx.tcx.struct_tail(item_ty).sty {
 376                 forbid_unsized = false;
 377             }
 378         }
 379
 380         fcx.register_wf_obligation(item_ty, ty_span, ObligationCauseCode::MiscObligation);
 381         if forbid_unsized {
 382             fcx.register_bound(
 383                 item_ty,
 384                 fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem),
 385                 traits::ObligationCause::new(ty_span, fcx.body_id, traits::MiscObligation),
 386             );
 387         }
 388
 389         // No implied bounds in a const, etc.
 390         vec![]
 391     });
 392 }
 393
 394 fn check_impl<'tcx>(
 395     tcx: TyCtxt<'tcx, 'tcx>,
 396     item: &hir::Item,
 397     ast_self_ty: &hir::Ty,
 398     ast_trait_ref: &Option<hir::TraitRef>,
 399 ) {
 400     debug!("check_impl: {:?}", item);
 401
 402     for_item(tcx, item).with_fcx(|fcx, tcx| {
 403         let item_def_id = fcx.tcx.hir().local_def_id_from_hir_id(item.hir_id);
 404
 405         match *ast_trait_ref {
 406             Some(ref ast_trait_ref) => {
 407                 let trait_ref = fcx.tcx.impl_trait_ref(item_def_id).unwrap();
 408                 let trait_ref =
 409                     fcx.normalize_associated_types_in(
 410                         ast_trait_ref.path.span, &trait_ref);
 411                 let obligations =
 412                     ty::wf::trait_obligations(fcx,
 413                                                 fcx.param_env,
 414                                                 fcx.body_id,
 415                                                 &trait_ref,
 416                                                 ast_trait_ref.path.span);
 417                 for obligation in obligations {
 418                     fcx.register_predicate(obligation);
 419                 }
 420             }
 421             None => {
 422                 let self_ty = fcx.tcx.type_of(item_def_id);
 423                 let self_ty = fcx.normalize_associated_types_in(item.span, &self_ty);
 424                 fcx.register_wf_obligation(self_ty, ast_self_ty.span,
 425                     ObligationCauseCode::MiscObligation);
 426             }
 427         }
 428
 429         check_where_clauses(tcx, fcx, item.span, item_def_id, None);
 430
 431         fcx.impl_implied_bounds(item_def_id, item.span)
 432     });
 433 }
 434
 435 /// Checks where-clauses and inline bounds that are declared on `def_id`.
 436 fn check_where_clauses<'gcx, 'fcx, 'tcx>(
 437     tcx: TyCtxt<'gcx, 'gcx>,
 438     fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 439     span: Span,
 440     def_id: DefId,
 441     return_ty: Option<Ty<'tcx>>,
 442 ) {
 443     debug!("check_where_clauses(def_id={:?}, return_ty={:?})", def_id, return_ty);
 444
 445     let predicates = fcx.tcx.predicates_of(def_id);
 446     let generics = tcx.generics_of(def_id);
 447
 448     let is_our_default = |def: &ty::GenericParamDef| {
 449         match def.kind {
 450             GenericParamDefKind::Type { has_default, .. } => {
 451                 has_default && def.index >= generics.parent_count as u32
 452             }
 453             _ => unreachable!()
 454         }
 455     };
 456
 457     // Check that concrete defaults are well-formed. See test `type-check-defaults.rs`.
 458     // For example, this forbids the declaration:
 459     //
 460     //     struct Foo<T = Vec<[u32]>> { .. }
 461     //
 462     // Here, the default `Vec<[u32]>` is not WF because `[u32]: Sized` does not hold.
 463     for param in &generics.params {
 464         if let GenericParamDefKind::Type { .. } = param.kind {
 465             if is_our_default(&param) {
 466                 let ty = fcx.tcx.type_of(param.def_id);
 467                 // Ignore dependent defaults -- that is, where the default of one type
 468                 // parameter includes another (e.g., `<T, U = T>`). In those cases, we can't
 469                 // be sure if it will error or not as user might always specify the other.
 470                 if !ty.needs_subst() {
 471                     fcx.register_wf_obligation(ty, fcx.tcx.def_span(param.def_id),
 472                         ObligationCauseCode::MiscObligation);
 473                 }
 474             }
 475         }
 476     }
 477
 478     // Check that trait predicates are WF when params are substituted by their defaults.
 479     // We don't want to overly constrain the predicates that may be written but we want to
 480     // catch cases where a default my never be applied such as `struct Foo<T: Copy = String>`.
 481     // Therefore we check if a predicate which contains a single type param
 482     // with a concrete default is WF with that default substituted.
 483     // For more examples see tests `defaults-well-formedness.rs` and `type-check-defaults.rs`.
 484     //
 485     // First we build the defaulted substitution.
 486     let substs = InternalSubsts::for_item(fcx.tcx, def_id, |param, _| {
 487         match param.kind {
 488             GenericParamDefKind::Lifetime => {
 489                 // All regions are identity.
 490                 fcx.tcx.mk_param_from_def(param)
 491             }
 492
 493             GenericParamDefKind::Type { .. } => {
 494                 // If the param has a default, ...
 495                 if is_our_default(param) {
 496                     let default_ty = fcx.tcx.type_of(param.def_id);
 497                     // ... and it's not a dependent default, ...
 498                     if !default_ty.needs_subst() {
 499                         // ... then substitute it with the default.
 500                         return default_ty.into();
 501                     }
 502                 }
 503                 // Mark unwanted params as error.
 504                 fcx.tcx.types.err.into()
 505             }
 506
 507             GenericParamDefKind::Const => {
 508                 // FIXME(const_generics:defaults)
 509                 fcx.tcx.consts.err.into()
 510             }
 511         }
 512     });
 513
 514     // Now we build the substituted predicates.
 515     let default_obligations = predicates.predicates.iter().flat_map(|&(pred, _)| {
 516         #[derive(Default)]
 517         struct CountParams { params: FxHashSet<u32> }
 518         impl<'tcx> ty::fold::TypeVisitor<'tcx> for CountParams {
 519             fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
 520                 if let ty::Param(param) = t.sty {
 521                     self.params.insert(param.index);
 522                 }
 523                 t.super_visit_with(self)
 524             }
 525
 526             fn visit_region(&mut self, _: ty::Region<'tcx>) -> bool {
 527                 true
 528             }
 529
 530             fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> bool {
 531                 if let ConstValue::Param(param) = c.val {
 532                     self.params.insert(param.index);
 533                 }
 534                 c.super_visit_with(self)
 535             }
 536         }
 537         let mut param_count = CountParams::default();
 538         let has_region = pred.visit_with(&mut param_count);
 539         let substituted_pred = pred.subst(fcx.tcx, substs);
 540         // Don't check non-defaulted params, dependent defaults (including lifetimes)
 541         // or preds with multiple params.
 542         if substituted_pred.references_error() || param_count.params.len() > 1 || has_region {
 543             None
 544         } else if predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
 545             // Avoid duplication of predicates that contain no parameters, for example.
 546             None
 547         } else {
 548             Some(substituted_pred)
 549         }
 550     }).map(|pred| {
 551         // Convert each of those into an obligation. So if you have
 552         // something like `struct Foo<T: Copy = String>`, we would
 553         // take that predicate `T: Copy`, substitute to `String: Copy`
 554         // (actually that happens in the previous `flat_map` call),
 555         // and then try to prove it (in this case, we'll fail).
 556         //
 557         // Note the subtle difference from how we handle `predicates`
 558         // below: there, we are not trying to prove those predicates
 559         // to be *true* but merely *well-formed*.
 560         let pred = fcx.normalize_associated_types_in(span, &pred);
 561         let cause = traits::ObligationCause::new(span, fcx.body_id, traits::ItemObligation(def_id));
 562         traits::Obligation::new(cause, fcx.param_env, pred)
 563     });
 564
 565     let mut predicates = predicates.instantiate_identity(fcx.tcx);
 566
 567     if let Some(return_ty) = return_ty {
 568         predicates.predicates.extend(check_existential_types(tcx, fcx, def_id, span, return_ty));
 569     }
 570
 571     let predicates = fcx.normalize_associated_types_in(span, &predicates);
 572
 573     debug!("check_where_clauses: predicates={:?}", predicates.predicates);
 574     let wf_obligations =
 575         predicates.predicates
 576                     .iter()
 577                     .flat_map(|p| ty::wf::predicate_obligations(fcx,
 578                                                                 fcx.param_env,
 579                                                                 fcx.body_id,
 580                                                                 p,
 581                                                                 span));
 582
 583     for obligation in wf_obligations.chain(default_obligations) {
 584         debug!("next obligation cause: {:?}", obligation.cause);
 585         fcx.register_predicate(obligation);
 586     }
 587 }
 588
 589 fn check_fn_or_method<'fcx, 'gcx, 'tcx>(
 590     tcx: TyCtxt<'gcx, 'gcx>,
 591     fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 592     span: Span,
 593     sig: ty::PolyFnSig<'tcx>,
 594     def_id: DefId,
 595     implied_bounds: &mut Vec<Ty<'tcx>>,
 596 ) {
 597     let sig = fcx.normalize_associated_types_in(span, &sig);
 598     let sig = fcx.tcx.liberate_late_bound_regions(def_id, &sig);
 599
 600     for input_ty in sig.inputs() {
 601         fcx.register_wf_obligation(&input_ty, span, ObligationCauseCode::MiscObligation);
 602     }
 603     implied_bounds.extend(sig.inputs());
 604
 605     fcx.register_wf_obligation(sig.output(), span, ObligationCauseCode::MiscObligation);
 606
 607     // FIXME(#25759) return types should not be implied bounds
 608     implied_bounds.push(sig.output());
 609
 610     check_where_clauses(tcx, fcx, span, def_id, Some(sig.output()));
 611 }
 612
 613 /// Checks "defining uses" of existential types to ensure that they meet the restrictions laid for
 614 /// "higher-order pattern unification".
 615 /// This ensures that inference is tractable.
 616 /// In particular, definitions of existential types can only use other generics as arguments,
 617 /// and they cannot repeat an argument. Example:
 618 ///
 619 /// ```rust
 620 /// existential type Foo<A, B>;
 621 ///
 622 /// // Okay -- `Foo` is applied to two distinct, generic types.
 623 /// fn a<T, U>() -> Foo<T, U> { .. }
 624 ///
 625 /// // Not okay -- `Foo` is applied to `T` twice.
 626 /// fn b<T>() -> Foo<T, T> { .. }
 627 ///
 628 /// // Not okay -- `Foo` is applied to a non-generic type.
 629 /// fn b<T>() -> Foo<T, u32> { .. }
 630 /// ```
 631 ///
 632 fn check_existential_types<'fcx, 'gcx, 'tcx>(
 633     tcx: TyCtxt<'gcx, 'gcx>,
 634     fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 635     fn_def_id: DefId,
 636     span: Span,
 637     ty: Ty<'tcx>,
 638 ) -> Vec<ty::Predicate<'tcx>> {
 639     trace!("check_existential_types(ty={:?})", ty);
 640     let mut substituted_predicates = Vec::new();
 641     ty.fold_with(&mut ty::fold::BottomUpFolder {
 642         tcx: fcx.tcx,
 643         ty_op: |ty| {
 644             if let ty::Opaque(def_id, substs) = ty.sty {
 645                 trace!("check_existential_types: opaque_ty, {:?}, {:?}", def_id, substs);
 646                 let generics = tcx.generics_of(def_id);
 647                 // Only check named existential types defined in this crate.
 648                 if generics.parent.is_none() && def_id.is_local() {
 649                     let opaque_hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
 650                     if may_define_existential_type(tcx, fn_def_id, opaque_hir_id) {
 651                         trace!("check_existential_types: may define, generics={:#?}", generics);
 652                         let mut seen: FxHashMap<_, Vec<_>> = FxHashMap::default();
 653                         for (subst, param) in substs.iter().zip(&generics.params) {
 654                             match subst.unpack() {
 655                                 ty::subst::UnpackedKind::Type(ty) => match ty.sty {
 656                                     ty::Param(..) => {}
 657                                     // Prevent `fn foo() -> Foo<u32>` from being defining.
 658                                     _ => {
 659                                         tcx.sess
 660                                             .struct_span_err(
 661                                                 span,
 662                                                 "non-defining existential type use \
 663                                                  in defining scope",
 664                                             )
 665                                             .span_note(
 666                                                 tcx.def_span(param.def_id),
 667                                                 &format!(
 668                                                     "used non-generic type {} for \
 669                                                      generic parameter",
 670                                                     ty,
 671                                                 ),
 672                                             )
 673                                             .emit();
 674                                     }
 675                                 }
 676
 677                                 ty::subst::UnpackedKind::Lifetime(region) => {
 678                                     let param_span = tcx.def_span(param.def_id);
 679                                     if let ty::ReStatic = region {
 680                                         tcx
 681                                             .sess
 682                                             .struct_span_err(
 683                                                 span,
 684                                                 "non-defining existential type use \
 685                                                     in defining scope",
 686                                             )
 687                                             .span_label(
 688                                                 param_span,
 689                                                 "cannot use static lifetime, use a bound lifetime \
 690                                                 instead or remove the lifetime parameter from the \
 691                                                 existential type",
 692                                             )
 693                                             .emit();
 694                                     } else {
 695                                         seen.entry(region).or_default().push(param_span);
 696                                     }
 697                                 }
 698
 699                                 ty::subst::UnpackedKind::Const(ct) => match ct.val {
 700                                     ConstValue::Param(_) => {}
 701                                     _ => {
 702                                         tcx.sess
 703                                             .struct_span_err(
 704                                                 span,
 705                                                 "non-defining existential type use \
 706                                                 in defining scope",
 707                                             )
 708                                             .span_note(
 709                                                 tcx.def_span(param.def_id),
 710                                                 &format!(
 711                                                     "used non-generic const {} for \
 712                                                     generic parameter",
 713                                                     ty,
 714                                                 ),
 715                                             )
 716                                             .emit();
 717                                     }
 718                                 }
 719                             } // match subst
 720                         } // for (subst, param)
 721                         for (_, spans) in seen {
 722                             if spans.len() > 1 {
 723                                 tcx
 724                                     .sess
 725                                     .struct_span_err(
 726                                         span,
 727                                         "non-defining existential type use \
 728                                             in defining scope",
 729                                     ).
 730                                     span_note(
 731                                         spans,
 732                                         "lifetime used multiple times",
 733                                     )
 734                                     .emit();
 735                             }
 736                         }
 737                     } // if may_define_existential_type
 738
 739                     // Now register the bounds on the parameters of the existential type
 740                     // so the parameters given by the function need to fulfill them.
 741                     //
 742                     //     existential type Foo<T: Bar>: 'static;
 743                     //     fn foo<U>() -> Foo<U> { .. *}
 744                     //
 745                     // becomes
 746                     //
 747                     //     existential type Foo<T: Bar>: 'static;
 748                     //     fn foo<U: Bar>() -> Foo<U> { .. *}
 749                     let predicates = tcx.predicates_of(def_id);
 750                     trace!(
 751                         "check_existential_types: may define, predicates={:#?}",
 752                         predicates,
 753                     );
 754                     for &(pred, _) in predicates.predicates.iter() {
 755                         let substituted_pred = pred.subst(fcx.tcx, substs);
 756                         // Avoid duplication of predicates that contain no parameters, for example.
 757                         if !predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
 758                             substituted_predicates.push(substituted_pred);
 759                         }
 760                     }
 761                 } // if is_named_existential_type
 762             } // if let Opaque
 763             ty
 764         },
 765         lt_op: |lt| lt,
 766         ct_op: |ct| ct,
 767     });
 768     substituted_predicates
 769 }
 770
 771 fn check_method_receiver<'fcx, 'gcx, 'tcx>(fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 772                                            method_sig: &hir::MethodSig,
 773                                            method: &ty::AssocItem,
 774                                            self_ty: Ty<'tcx>)
 775 {
 776     // Check that the method has a valid receiver type, given the type `Self`.
 777     debug!("check_method_receiver({:?}, self_ty={:?})",
 778            method, self_ty);
 779
 780     if !method.method_has_self_argument {
 781         return;
 782     }
 783
 784     let span = method_sig.decl.inputs[0].span;
 785
 786     let sig = fcx.tcx.fn_sig(method.def_id);
 787     let sig = fcx.normalize_associated_types_in(span, &sig);
 788     let sig = fcx.tcx.liberate_late_bound_regions(method.def_id, &sig);
 789
 790     debug!("check_method_receiver: sig={:?}", sig);
 791
 792     let self_ty = fcx.normalize_associated_types_in(span, &self_ty);
 793     let self_ty = fcx.tcx.liberate_late_bound_regions(
 794         method.def_id,
 795         &ty::Binder::bind(self_ty)
 796     );
 797
 798     let receiver_ty = sig.inputs()[0];
 799
 800     let receiver_ty = fcx.normalize_associated_types_in(span, &receiver_ty);
 801     let receiver_ty = fcx.tcx.liberate_late_bound_regions(
 802         method.def_id,
 803         &ty::Binder::bind(receiver_ty)
 804     );
 805
 806     if fcx.tcx.features().arbitrary_self_types {
 807         if !receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
 808             // Report error; `arbitrary_self_types` was enabled.
 809             fcx.tcx.sess.diagnostic().mut_span_err(
 810                 span, &format!("invalid method receiver type: {:?}", receiver_ty)
 811             ).note("type of `self` must be `Self` or a type that dereferences to it")
 812             .help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 813             .code(DiagnosticId::Error("E0307".into()))
 814             .emit();
 815         }
 816     } else {
 817         if !receiver_is_valid(fcx, span, receiver_ty, self_ty, false) {
 818             if receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
 819                 // Report error; would have worked with `arbitrary_self_types`.
 820                 feature_gate::feature_err(
 821                     &fcx.tcx.sess.parse_sess,
 822                     sym::arbitrary_self_types,
 823                     span,
 824                     GateIssue::Language,
 825                     &format!(
 826                         "`{}` cannot be used as the type of `self` without \
 827                             the `arbitrary_self_types` feature",
 828                         receiver_ty,
 829                     ),
 830                 ).help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 831                 .emit();
 832             } else {
 833                 // Report error; would not have worked with `arbitrary_self_types`.
 834                 fcx.tcx.sess.diagnostic().mut_span_err(
 835                     span, &format!("invalid method receiver type: {:?}", receiver_ty)
 836                 ).note("type must be `Self` or a type that dereferences to it")
 837                 .help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 838                 .code(DiagnosticId::Error("E0307".into()))
 839                 .emit();
 840             }
 841         }
 842     }
 843 }
 844
 845 /// Returns whether `receiver_ty` would be considered a valid receiver type for `self_ty`. If
 846 /// `arbitrary_self_types` is enabled, `receiver_ty` must transitively deref to `self_ty`, possibly
 847 /// through a `*const/mut T` raw pointer. If the feature is not enabled, the requirements are more
 848 /// strict: `receiver_ty` must implement `Receiver` and directly implement
 849 /// `Deref<Target = self_ty>`.
 850 ///
 851 /// N.B., there are cases this function returns `true` but causes an error to be emitted,
 852 /// particularly when `receiver_ty` derefs to a type that is the same as `self_ty` but has the
 853 /// wrong lifetime. Be careful of this if you are calling this function speculatively.
 854 fn receiver_is_valid<'fcx, 'tcx, 'gcx>(
 855     fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 856     span: Span,
 857     receiver_ty: Ty<'tcx>,
 858     self_ty: Ty<'tcx>,
 859     arbitrary_self_types_enabled: bool,
 860 ) -> bool {
 861     let cause = fcx.cause(span, traits::ObligationCauseCode::MethodReceiver);
 862
 863     let can_eq_self = |ty| fcx.infcx.can_eq(fcx.param_env, self_ty, ty).is_ok();
 864
 865     // `self: Self` is always valid.
 866     if can_eq_self(receiver_ty) {
 867         if let Some(mut err) = fcx.demand_eqtype_with_origin(&cause, self_ty, receiver_ty) {
 868             err.emit();
 869         }
 870         return true
 871     }
 872
 873     let mut autoderef = fcx.autoderef(span, receiver_ty);
 874
 875     // The `arbitrary_self_types` feature allows raw pointer receivers like `self: *const Self`.
 876     if arbitrary_self_types_enabled {
 877         autoderef = autoderef.include_raw_pointers();
 878     }
 879
 880     // The first type is `receiver_ty`, which we know its not equal to `self_ty`; skip it.
 881     autoderef.next();
 882
 883     // Keep dereferencing `receiver_ty` until we get to `self_ty`.
 884     loop {
 885         if let Some((potential_self_ty, _)) = autoderef.next() {
 886             debug!("receiver_is_valid: potential self type `{:?}` to match `{:?}`",
 887                 potential_self_ty, self_ty);
 888
 889             if can_eq_self(potential_self_ty) {
 890                 autoderef.finalize(fcx);
 891
 892                 if let Some(mut err) = fcx.demand_eqtype_with_origin(
 893                     &cause, self_ty, potential_self_ty
 894                 ) {
 895                     err.emit();
 896                 }
 897
 898                 break
 899             }
 900         } else {
 901             debug!("receiver_is_valid: type `{:?}` does not deref to `{:?}`",
 902                 receiver_ty, self_ty);
 903             // If he receiver already has errors reported due to it, consider it valid to avoid
 904             // unecessary errors (#58712).
 905             return receiver_ty.references_error();
 906         }
 907
 908         // Without the `arbitrary_self_types` feature, `receiver_ty` must directly deref to
 909         // `self_ty`. Enforce this by only doing one iteration of the loop.
 910         if !arbitrary_self_types_enabled {
 911             return false
 912         }
 913     }
 914
 915     // Without `feature(arbitrary_self_types)`, we require that `receiver_ty` implements `Receiver`.
 916     if !arbitrary_self_types_enabled {
 917         let trait_def_id = match fcx.tcx.lang_items().receiver_trait() {
 918             Some(did) => did,
 919             None => {
 920                 debug!("receiver_is_valid: missing Receiver trait");
 921                 return false
 922             }
 923         };
 924
 925         let trait_ref = ty::TraitRef{
 926             def_id: trait_def_id,
 927             substs: fcx.tcx.mk_substs_trait(receiver_ty, &[]),
 928         };
 929
 930         let obligation = traits::Obligation::new(
 931             cause.clone(),
 932             fcx.param_env,
 933             trait_ref.to_predicate()
 934         );
 935
 936         if !fcx.predicate_must_hold_modulo_regions(&obligation) {
 937             debug!("receiver_is_valid: type `{:?}` does not implement `Receiver` trait",
 938                 receiver_ty);
 939             return false
 940         }
 941     }
 942
 943     true
 944 }
 945
 946 fn check_variances_for_type_defn<'tcx>(
 947     tcx: TyCtxt<'tcx, 'tcx>,
 948     item: &hir::Item,
 949     hir_generics: &hir::Generics,
 950 ) {
 951     let item_def_id = tcx.hir().local_def_id_from_hir_id(item.hir_id);
 952     let ty = tcx.type_of(item_def_id);
 953     if tcx.has_error_field(ty) {
 954         return;
 955     }
 956
 957     let ty_predicates = tcx.predicates_of(item_def_id);
 958     assert_eq!(ty_predicates.parent, None);
 959     let variances = tcx.variances_of(item_def_id);
 960
 961     let mut constrained_parameters: FxHashSet<_> =
 962         variances.iter().enumerate()
 963                         .filter(|&(_, &variance)| variance != ty::Bivariant)
 964                         .map(|(index, _)| Parameter(index as u32))
 965                         .collect();
 966
 967     identify_constrained_generic_params(
 968         tcx,
 969         &ty_predicates,
 970         None,
 971         &mut constrained_parameters,
 972     );
 973
 974     for (index, _) in variances.iter().enumerate() {
 975         if constrained_parameters.contains(&Parameter(index as u32)) {
 976             continue;
 977         }
 978
 979         let param = &hir_generics.params[index];
 980
 981         match param.name {
 982             hir::ParamName::Error => { }
 983             _ => report_bivariance(tcx, param.span, param.name.ident().name),
 984         }
 985     }
 986 }
 987
 988 fn report_bivariance<'tcx>(tcx: TyCtxt<'tcx, 'tcx>, span: Span, param_name: ast::Name) {
 989     let mut err = error_392(tcx, span, param_name);
 990
 991     let suggested_marker_id = tcx.lang_items().phantom_data();
 992     // Help is available only in presence of lang items.
 993     if let Some(def_id) = suggested_marker_id {
 994         err.help(&format!("consider removing `{}` or using a marker such as `{}`",
 995                           param_name,
 996                           tcx.def_path_str(def_id)));
 997     }
 998     err.emit();
 999 }
1000
1001 fn reject_shadowing_parameters(tcx: TyCtxt<'_, '_>, def_id: DefId) {
1002     let generics = tcx.generics_of(def_id);
1003     let parent = tcx.generics_of(generics.parent.unwrap());
1004     let impl_params: FxHashMap<_, _> = parent.params.iter().flat_map(|param| match param.kind {
1005         GenericParamDefKind::Lifetime => None,
1006         GenericParamDefKind::Type { .. } | GenericParamDefKind::Const => {
1007             Some((param.name, param.def_id))
1008         }
1009     }).collect();
1010
1011     for method_param in &generics.params {
1012         // Shadowing is checked in `resolve_lifetime`.
1013         if let GenericParamDefKind::Lifetime = method_param.kind {
1014             continue
1015         }
1016         if impl_params.contains_key(&method_param.name) {
1017             // Tighten up the span to focus on only the shadowing type.
1018             let type_span = tcx.def_span(method_param.def_id);
1019
1020             // The expectation here is that the original trait declaration is
1021             // local so it should be okay to just unwrap everything.
1022             let trait_def_id = impl_params[&method_param.name];
1023             let trait_decl_span = tcx.def_span(trait_def_id);
1024             error_194(tcx, type_span, trait_decl_span, &method_param.name.as_str()[..]);
1025         }
1026     }
1027 }
1028
1029 /// Feature gates RFC 2056 -- trivial bounds, checking for global bounds that
1030 /// aren't true.
1031 fn check_false_global_bounds<'a, 'gcx, 'tcx>(
1032     fcx: &FnCtxt<'a, 'gcx, 'tcx>,
1033     span: Span,
1034     id: hir::HirId)
1035 {
1036     let empty_env = ty::ParamEnv::empty();
1037
1038     let def_id = fcx.tcx.hir().local_def_id_from_hir_id(id);
1039     let predicates = fcx.tcx.predicates_of(def_id).predicates
1040         .iter()
1041         .map(|(p, _)| *p)
1042         .collect();
1043     // Check elaborated bounds.
1044     let implied_obligations = traits::elaborate_predicates(fcx.tcx, predicates);
1045
1046     for pred in implied_obligations {
1047         // Match the existing behavior.
1048         if pred.is_global() && !pred.has_late_bound_regions() {
1049             let pred = fcx.normalize_associated_types_in(span, &pred);
1050             let obligation = traits::Obligation::new(
1051                 traits::ObligationCause::new(
1052                     span,
1053                     id,
1054                     traits::TrivialBound,
1055                 ),
1056                 empty_env,
1057                 pred,
1058             );
1059             fcx.register_predicate(obligation);
1060         }
1061     }
1062
1063     fcx.select_all_obligations_or_error();
1064 }
1065
1066 pub struct CheckTypeWellFormedVisitor<'tcx> {
1067     tcx: TyCtxt<'tcx, 'tcx>,
1068 }
1069
1070 impl CheckTypeWellFormedVisitor<'gcx> {
1071     pub fn new(tcx: TyCtxt<'gcx, 'gcx>) -> CheckTypeWellFormedVisitor<'gcx> {
1072         CheckTypeWellFormedVisitor {
1073             tcx,
1074         }
1075     }
1076 }
1077
1078 impl ParItemLikeVisitor<'tcx> for CheckTypeWellFormedVisitor<'tcx> {
1079     fn visit_item(&self, i: &'tcx hir::Item) {
1080         debug!("visit_item: {:?}", i);
1081         let def_id = self.tcx.hir().local_def_id_from_hir_id(i.hir_id);
1082         self.tcx.ensure().check_item_well_formed(def_id);
1083     }
1084
1085     fn visit_trait_item(&self, trait_item: &'tcx hir::TraitItem) {
1086         debug!("visit_trait_item: {:?}", trait_item);
1087         let def_id = self.tcx.hir().local_def_id_from_hir_id(trait_item.hir_id);
1088         self.tcx.ensure().check_trait_item_well_formed(def_id);
1089     }
1090
1091     fn visit_impl_item(&self, impl_item: &'tcx hir::ImplItem) {
1092         debug!("visit_impl_item: {:?}", impl_item);
1093         let def_id = self.tcx.hir().local_def_id_from_hir_id(impl_item.hir_id);
1094         self.tcx.ensure().check_impl_item_well_formed(def_id);
1095     }
1096 }
1097
1098 ///////////////////////////////////////////////////////////////////////////
1099 // ADT
1100
1101 struct AdtVariant<'tcx> {
1102     fields: Vec<AdtField<'tcx>>,
1103 }
1104
1105 struct AdtField<'tcx> {
1106     ty: Ty<'tcx>,
1107     span: Span,
1108 }
1109
1110 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
1111     fn non_enum_variant(&self, struct_def: &hir::VariantData) -> AdtVariant<'tcx> {
1112         let fields = struct_def.fields().iter().map(|field| {
1113             let field_ty = self.tcx.type_of(self.tcx.hir().local_def_id_from_hir_id(field.hir_id));
1114             let field_ty = self.normalize_associated_types_in(field.span,
1115                                                               &field_ty);
1116             AdtField { ty: field_ty, span: field.span }
1117         })
1118         .collect();
1119         AdtVariant { fields }
1120     }
1121
1122     fn enum_variants(&self, enum_def: &hir::EnumDef) -> Vec<AdtVariant<'tcx>> {
1123         enum_def.variants.iter()
1124             .map(|variant| self.non_enum_variant(&variant.node.data))
1125             .collect()
1126     }
1127
1128     fn impl_implied_bounds(&self, impl_def_id: DefId, span: Span) -> Vec<Ty<'tcx>> {
1129         match self.tcx.impl_trait_ref(impl_def_id) {
1130             Some(ref trait_ref) => {
1131                 // Trait impl: take implied bounds from all types that
1132                 // appear in the trait reference.
1133                 let trait_ref = self.normalize_associated_types_in(span, trait_ref);
1134                 trait_ref.substs.types().collect()
1135             }
1136
1137             None => {
1138                 // Inherent impl: take implied bounds from the `self` type.
1139                 let self_ty = self.tcx.type_of(impl_def_id);
1140                 let self_ty = self.normalize_associated_types_in(span, &self_ty);
1141                 vec![self_ty]
1142             }
1143         }
1144     }
1145 }
1146
1147 fn error_392<'tcx>(
1148     tcx: TyCtxt<'tcx, 'tcx>,
1149     span: Span,
1150     param_name: ast::Name,
1151 ) -> DiagnosticBuilder<'tcx> {
1152     let mut err = struct_span_err!(tcx.sess, span, E0392,
1153                   "parameter `{}` is never used", param_name);
1154     err.span_label(span, "unused parameter");
1155     err
1156 }
1157
1158 fn error_194(tcx: TyCtxt<'_, '_>, span: Span, trait_decl_span: Span, name: &str) {
1159     struct_span_err!(tcx.sess, span, E0194,
1160                      "type parameter `{}` shadows another type parameter of the same name",
1161                      name)
1162         .span_label(span, "shadows another type parameter")
1163         .span_label(trait_decl_span, format!("first `{}` declared here", name))
1164         .emit();
1165 }